CFITSIO is a library of C and Fortran subroutines for reading and writing data
files in FITS (Flexible Image Transport System) data format. CFITSIO provides
simple high-level routines for reading and writing FITS files that insulate the
programmer from the internal complexities of the FITS format. CFITSIO also
provides many advanced features for manipulating and filtering the information
in FITS files.

WWW: https://heasarc.gsfc.nasa.gov/docs/software/fitsio/